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Photosynthesis

Photosynthesis. Ch. 6.1 (part 2)- Light Dependent Reactions. Target #6: I can identify the steps of the light-dependent reactions. Step 1: The sunlight strikes photosystem II in the thylakoid membranes

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Photosynthesis

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  1. Photosynthesis Ch. 6.1 (part 2)- Light Dependent Reactions

  2. Target #6: I can identify the steps of the light-dependent reactions Step 1: The sunlight strikes photosystem II in the thylakoid membranes Photosystem: a pigment complex, like chlorophyll, and the electron acceptor in the thylakoid membrane The light energy is transferred into electrons

  3. Target #6- cont. • Step 2: The highly energized electrons are passed from photosystem II to an electron transport chain • Electron Transport Chain: a series of proteins embedded in the thylakoid membrane • Each protein in the chain passes the energized electrons along • At each protein the electron loses energy • Lost energy is used to make • H+ ions are formed from water splitting through hydrolysis • ATP from ADP when H+ moves down the concentration gradient

  4. Target #6- cont. • Step 3 • Used electrons from photosystem II replace lost electrons in photosystem I. • Light strikes photosystem I in the thylakoid membrane • Charged electrons moved down a 2nd electron transport chain

  5. Target #6- cont. • Step 4: the electron is transferred from the second electron transport chain to the stroma of the chlorolast • An electron carrier molecule passes 2 electrons to NADP+ • When it picks up the electron, it also combines with a “free floating” H+ ion • This makes NADPH

  6. Some of the charged electrons will return to chlorophyll or leave for the light-independent reactions • The electrons need to be replaced • Chlorophyll would be unable to absorb light and the light-dependent reactions will stop • To replace lost electrons, water molecules are split • H+ ions from water molecules in a process called hydrolysis • H+ are moved into the thylakoid against the gradient • Move through ATP synthase protein complexes Target #7- I can describe how electrons are restored to the chloroplasts

  7. Photosynthesis Light Independent Reactions

  8. Target #8- I can describe the Calvin Cycle • The second phase of photosynthesis does not require light • Calvin Cycle: a series of reactions that use carbon dioxide to form carbohydrates • Takes place in the stroma of the chloroplast • It is a cycle because one of the last products can be used to start the process over again • Carbon fixation • Incorporation of CO2 molecules into organic compounds • 3 CO2 are needed to enter the Calvin cycle

  9. Target #9- I can identify the steps of the Calvin Cycle • Step 1: Carbon Fixation • One carbon atom from CO2 is added to a 5-carbon sugar known as RuBP • Needs to use enzyme Rubisco • Added carbon creates an unstable 6-carbon sugar

  10. Target #9- cont. • Step 2 • The 6-carbon sugar formed in step 1 is split into two 3-carbon molecules called PGA • The two molecules of PGA is converted into PGAL • ATP and NADPH are used to add energy to the two PGA molecules • ATP turns back into ADP • NADPH turns back into NADP+ • Recycled back to the light-dependent stage

  11. Step 3: • One PGAL molecule is recycled and turned back into the 5-carbon RuBP molecule to start the process over. • Uses phosphate groups from ATP • The second PGAL molecule leaves the cycle • After several cycles, the exited molecules combine to form glucose Target #9- Cont.

  12. Factors that Affect Photosynthesis • Light Intensity • The higher the intensity of light, the higher the rate of photosynthesis • There is a maximum rate of photosynthesis that can be reached • Carbon Dioxide • An increase of CO2 increases the rate of photosynthesis • Temperature • Increasing temperature accelerates the chemical reactions involved in photosynthesis • Rate of photosynthesis increases as the temperature increases • Does not apply to C4 and CAM plants • Closed stomata slow the rate of photosynthesis regardless of temperature Target #10- I can identify the factors that affect photosynthesis

  13. Target #11- I can describe stomata • Stomata • Pores in plants which allow water to be released into the air • Located on the underside of leaves • The major passageways for the exchange of CO2 and O2 • When a plant has a low CO2 level and a high O2 level, carbon fixation can not happen • Prevents the Calvin Cycle from happening • Mediated by alternate pathways

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